Our U.S. Pat. No. 7,093,593 B2 issued Aug. 22, 2006 titled “Floating Solar Pool Heater” describes a soft, flexible, floating solar pool heater made of planar upper and lower films bonded together to form a thin inflatable central portion for providing the major solar heat gathering and heat transfer to the water and a thicker inflatable outer ring connected to the periphery of the central portion for providing flotation and greater rigidity. In a preferred embodiment, in the inflatable central portion, a plurality of spaced spot welds between the upper and lower films hold the films in close proximity when the central portion is inflated. The central portion should lie directly on the water to transfer the solar energy thereto.
With this design, it can be understood that inflation of the central portion causes the periphery of the central portion to radially shrink because the upper and lower films in the central area are pushed apart. This central shrinkage puts radially inward stress on the outer ring. The magnitude and locations of the radial stress on the outer ring is partly determined by the shape and locations of the bonds between the upper and lower film in the central portion and is partially determined by the inflation pressure with greater pressure producing greater stress.
Excessive inflation of the central portion, such as by initial over inflation by the user or by further expansion of the inflation gas as it warms in the sunlight, may cause the outer ring to upwardly buckle. Buckling of the outer ring is undesirable because the buckled portion of the outer ring lifts the central portion of the water such that solar energy is not optimally transferred to the water and also because the upwardly buckled portion is susceptible to being lifted by the wind such that the heater is more readily blown from the pool,
Therefore, it is desirable to have an improved floating solar pool heater that overcomes the tendency of the outer ring to buckle.